This invention relates to a data recording method in a card memory and, more particularly, to a method of storing a consumed amount of a predetermined value in a cardboard type memory device.
A card memory is widely used for recording telephone charges, carfares, number of copying times with a copying machine, etc. It is very convenient for customers to use such kinds of card memories instead of cash. When a customer makes a payment with a card memory, the consumed amount of value corresponding to the payment is recorded in the card memory. Thus when the total of the consumed amount reaches a predetermined maximum value, the card memory is handled as a spent-out one. In a case of a telephone card, for example, a number of calls is recorded in the card every time the customer makes a phone call. When the recorded number reaches a predetermined maximum number, the telephone card becomes a spent-out one. There are two kinds of memories applicable to a recording area of a memory card. The one is a changeable memory like a memory with magnetic material, and the other is an unchangeable permanent memory such as a fuse-type semiconductor memory, a laser fused memory, and a destroyed hologram memory.
When a changeable memory is applied to the card memory, the factor of freedom increases so that recording of any values in the card memory and changing of the recorded values can be made freely. However the factor of safety decreases so that there is some possibility of accidentally losing a recorded data and allowing a criminal to tamper with a recorded value. Therefore it is dangerous to record a lot of money on the card having a changeable memory.
On the other hand, when an unchangeable memory is applied to the card memory, the factor of safety increases because permanent records are formed on the face of the card. However the factor of freedom decreases because a value which can be recorded is restricted. For example, in a telephone card which is available for 10 telephone calls, 10 record bits of a through j are provided on the card as is shown in FIG. 1, which are marked one by one whenever one telephone call is made. When three telephone calls have been made, bits a, b, c are marked with marks X by some way as shown in FIG. 1. The data recording method described above is suitable for recording a number of telephone calls, train rides over a particular distance, copying times, etc. But the above described method is not suitable for recording purchase amounts for various goods with different prices or transportation fare for various distances. For example, in the telephone card shown in FIG. 1, one record bit corresponds to one telephone call or 10 Yens (Japanese currency), but the same data recording method cannot be applied to a purchase card which has to handle fractions of 10 Yens. In such a purchase card, it is possible to define one record bit as a unit Yens. However, in that case, 10,000 record bits are required when the maximum value of the card is set to 10,000 Yens. This number of bits is not reasonable.
As described above, the data recording method according to the prior art cannot simultaneously improve both the factors of safety and freedom so that method is not suitable for a card which requires both factors.